Journal Club: Therapeutic Administration of 131-I for Differentiated Thyroid Cancer: Radiation Dose to Ovaries and Outcome of Pregnancies

The journal club has been getting neglected recently. Trying to remedy that for this year.

From this month's JNM comes a paper on I-131 therapy and pregnancy, always a very hot issue. The paper is a follow-up to an earlier study from 1996 which said that I-131 exposure from thyroid therapy did not affect the outcome of subsequent pregnancies.

In the current paper, the number of patients with pregnancies within a year following 131I therapy was increased over the previous study (n=158 vs n=96) enabling better statistical analysis of the results.

One of the more interesting (I thought) results from the study was that the percentage of miscarriages following treatment for thyroid cancer (either surgical or radioiodine therapy) increased. However, the percentages were essentially the same whether the treatment was surgical or with radioiodine (20.7% vs 19%).

There are a lot of statistics and tables presented in the paper looking at a myriad of things. However, the bottom line is that the authors did not find any evidence to support a common precaution that female patients avoid becoming pregnant for one year following treatment for thyroid cancer.

Garsi J-P, Schlumberger M, Rubino C, et al. Therapeutic administration of 131I for differentiated thyroid cancer: radiation dose to ovaries and outcome of pregnancies. J Nucl Med. 2008;49:845-852

Abstract:

Radiation is known to be mutagenic. The present study updates a 10-y-old study regarding pregnancy outcome and the health of offspring of women previously exposed to radioiodine (131I) during thyroid carcinoma treatment, by doubling the number of pregnancies that occurred after exposure. Methods: Data on 2,673 pregnancies were obtained by interviewing female patients who were treated for thyroid carcinoma but had not received significant external radiation to the ovaries. Results: The incidence of miscarriages was 10% before any treatment for thyroid cancer; this percentage increased after surgery for thyroid cancer, both before (20%) and after (19%) 131I treatment, with no variation according to the cumulative dose. In contrast to previously reported data, miscarriages were not significantly more frequent in women treated with radioiodine during the year before conception, not even in women who had received more than 370 MBq during that year. The incidences of stillbirths, preterm births, low birth weight, congenital malformations, and death during the first year of life were not significantly different before and after 131I therapy. The incidences of thyroid and nonthyroid cancers were similar in children born either before or after the mother's exposure to radioiodine. Conclusion: There is no evidence that exposure to radioiodine affects the outcomes of subsequent pregnancies and offspring. The question as to whether the incidences of malformations and thyroid and nonthyroid cancers are related to gonadal irradiation remains to be established. The doubling dose is still being heatedly debated, and the value of 1 Gy as the doubling dose in humans should be reevaluated.